The deposition of thin films of pure metals, alloys and semiconductors is of central importance for the manufacturing of microelectronic devices. The materials are generally deposited by the thermal decomposition of volatile compounds (Chemical Vapor Deposition, CVD).
The chemical vapor deposition (CVD) of copper (Cu), silver (Ag), and gold (Au), commonly referred to as the coinage metals, has attracted substantial attention over the last decade. Apart from specialized, small scale applications like the design and repair of X-ray lithographic masks and the generation of monodisperse nanoclusters, the metals have also been attracting attention for use in the manufacturing of microelectronic devices. A fundamental problem resulting from the use of metals is their ohmic resistivity and the heat thus generated. The dissipation of the resistively generated heat has become a limiting factor for microcircuit manufacturing and has led to the replacement of the previously popular aluminum with copper.
CVD of the coinage metals is described in Nast R. et al. Chem. Ber. 1963, 96, 2127 and in Nast R. and Lepel, W. H., Chem. Ber. 1969, 102, 3224. Although the resulting complexes of the process described are too labile to act as good CVD precursors and are non-volatile due to their polymeric nature, they can be transformed into a new class of volatile Cu(I) complexes by reacting them with donor ligands.
Cu(II) complexes are suitable in the presence of reducing gases, most commonly hydrogen (H2) and the first copper CVD publication reported by van Hermert et al. J. Electrochem. Soc. 1965, 112, 1123 was based on this principle.
To this day, the deposition of copper, silver and gold, has almost exclusively relied on the diketonate complexes as described in James, A. M. et al. Inorg. Chem 1998, 37, 3785.
The deposition of the coinage metals benefits from the low thermodynamic stability of their respective oxides, carbides, nitrides and hydrides. As a result, reasonably pure metallic films of copper, silver and gold have been obtained from oxygen containing complexes as described, for example, in Nast et al. 1963; Nast et al. 1969; Lakshmanan, Sik and Gil, W. N., Thin Solid Films 1999, 338, 24; Edwards D. A., et al. Mater. Chem. 1999, 9, 1771; and Holl, M. M. B. et al., Inorg. Chem., 1994, 33, 510. The use of reactive gases, for example H2, and higher substrate temperatures can further reduce contamination with oxygen or carbon, but the presence of oxygen in the ligand is problematic due to the formation of copper oxides which increase the electrical resistance of the copper films because of their semiconductor nature. These same problems apply to other heteroelements like fluorine or phosphorous which are introduced to enhance the volatility of the complexes.
Amidinate complexes of Cu, Ag and Au have been described previously, for example in Kilner M. and Pietryszowski M., Polyhedron, 1983, 2, 1379; Cotton, F. A., et al., J. Am. Chem. Soc., 1988, 110, 7077; and Hartmann E. et al., Naturforsch, 1989, 44b, 1. However, such complexes are generally non-volatile tetramers of type Cu4L4 (L=amidine) or dimers that are rendered involatile by the presence of large aryl substituents.
This invention describes the synthesis and use of metal complexes of a specific class of oxygen free organic ligands, known as amidines, to achieve the deposition of a variety of different materials including metals and metal alloys. The deposition reactions are preferably conducted from the gas phase and at elevated temperatures.
Amidinate complexes have been described for a variety of metals but have not been used as precursors for the manufacturing of metals, alloys or metal based materials like metal oxides, metal carbides, etc.